PARENT SESSION
Oral Session #53: Elevated CO₂: Communities, ecosystems, soils.
Presiding: G. Lin
Wednesday, August 7. 8:00 AM to 11:30 AM. Coconino Meeting Room, TCC.

Long-term decomposition of Douglas-fir roots grown under elevated CO₂ and/or temperature treatments: implications for carbon sequestration .

CHEN, HUA^*,1, RYGIEWICZ, PAUL², JOHNSON, MARK², HARMON, MARK¹, ¹ Department of Forest Science, Oregon State University, Corvallis, OR² US EPA, Corvallis, OR

ABSTRACT- Elevated CO₂ and atmospheric warming may affect litter quality of plants and its subsequent decomposition in forested ecosystems. Little data are available to test this potential feedback on root tissues. In this study, we used the fine (diameter <2 mm) and small (2-10 mm) roots of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings grown for 4 years under ambient or elevated (+ 180 ppm) CO₂, and under ambient or elevated (+4.0 0C) temperature in outdoor, sun-lit, chambers for initial substrate quality analysis and subsequent field decomposition study. Four years of exposure to elevated CO₂ and/or elevated temperature did not have significant effect on the concentrations of N, water-soluble extractives, nonpolar extractives, cellulose, and lignin of root material. Roots in mesh litterbags were placed in Douglas-fir old-growth forests at the low (537 m) and high (1220 m) elevation field sites on the west slope of the Oregon Cascade Mountains. At each site, the decomposition rates of roots after two years under field conditions were very similar, regardless of the source of the roots, although the roots at low elevation site decomposed faster than those at high elevation site. Our results suggest that the negative feedback of elevated CO₂ changes in litter quality and subsequent decomposition is probably not important. The implications of this study for belowground carbon sequestration in coniferous forests at the Pacific Northwest will be discussed.

KEY WORDS: Elevated CO₂ , tissue quality , decomposition, carbon sequestration